Conventionally, wireless communication technologies have remarkably progressed and spread, and it is always desired to cultivate frequency resources. In 2010, it is expected that people use various wireless multimedia equipments, and, as a result, shortage of frequencies becomes a problem in various situations.
Predecessors have developed various modulation schemes, for example, ASK, PSK, CDMA and OFDM in order to improve efficiency of frequency use. A SSB (Single Side Band) scheme as disclosed in Patent Documents 1 and 2, for example, has been modified.
The modulation scheme that is said to have the highest efficiency of frequency use at present is a combination of OFDM and quadrature modulation, and its data transmission rate is 2 bit/sec/Hz.    Patent Document 1: U.S. Pat. No. 6,091,781 (Japanese Patent Application Laid-Open No. HEI11-239189)    Patent Document 2: Japanese Patent Application Laid-Open No. 2003-134069